The present invention relates to an insulating apparatus and a method of installing the apparatus, and particularly but not exclusively relates to an insulating apparatus and method of installing the apparatus for use in insulating oil and gas pipelines.
In the oil and gas exploration industry it is often necessary to transport oil and gas over long distances underwater. This is often done using a pipeline installed at or near the sea bed. In order to allow the oil to flow through the pipeline easily, it is usually necessary to keep the oil relatively hot (generally at a temperature of between 80° C. and 100° C.). Maintaining the oil at this temperature prevents “waxing” (solidification) of the oil from occurring whilst flowing through the pipeline, thereby helping to prevent blockages in the pipeline.
As the environment surrounding the pipeline is much cooler than the temperature of the oil flowing through it, it is beneficial to provide some form of insulation to surround the pipeline. This is often done using a pipe-in-pipe insulation system where an outer pipe (of greater diameter than the inner oil containing pipe) is positioned around the inner oil containing pipe such that a cavity is created between the two, the cavity typically being filled with an insulating material. Mineral wool offers a cost effective, and therefore widely used insulant for this purpose. One type of insulating unit is Fibashield™ offered by Rockwool Limited of Bridgend, Glamorgan, Wales, UK which consists of mineral wool insulant surrounded by a rigid polymer sheath. Sections of the insulating unit, approximately 2.5 metres long, are placed around the oil containing pipeline, either by sliding the insulating unit onto one end of the pipeline, or by cutting through one wall of the insulating unit along its longitudinal axis and “clipping” the unit over the pipeline section.
Annular ring centralisers such as those offered by Devol Engineering of Greenock, U.K., are spaced apart (typically by approximately 2.5 m) along the length of the longitudinal axis of each insulating unit, such that in use, the centralisers extend radially outwardly between the inner and outer pipe walls, and their purpose is to transfer load (e.g. gravity acting upon the inner oil containing pipe) from the inner pipe to the outer pipe without compressing the insulation material. The centralisers also therefore act to maintain the central longitudinal axis of the pipeline in a parallel and co-axial relationship with the longitudinal bore of the surrounding insulating material. This prevents the situation where the inner oil containing pipeline becomes closer to one wall of the outer pipe, and hence has poorer insulation at that point due to compression/destruction of the surrounding insulating material. Each section of pipeline and associated insulating unit(s) are typically transported and stored on large reels.
The problem with such insulation systems is that when in transit and/or storage on the reels, the compression exerted on the insulation at the inner radius or intrados of the curved length of insulation unit is sufficient to permanently deform the insulation. Therefore, when the length of insulation unit is off-loaded from the reel and is straightened, the non-elastic behaviour of the mineral wool results in areas where the insulation is reduced, typically between each centraliser location. This reduction in insulation is often substantial.